A typical prior art signalling receiver is disclosed in published German patent application DE-OS No. 33 43 646, which discloses a line signal analyzer in which the `a` and `b` wires of a telecommunications exchange line are connected through RC networks to a differential amplifier whose output is fed to a bandpass filter which is clocked from an adjustable clock generator. In that prior art arrangement, a band filter passing only the signal frequency to be received is implemented with a so-called switched-capacitor filter. In this manner, all signal frequencies to be received can be detected with a single filter and the respective midband frequency may be adjusted by a clock frequency applied over a clock line.